Revision 1.1
WebSwitch™ Users Manual
2.2.5 Temperature/Humidity Sensor Connection(Model XRDI-WS3P only)
Temperature and/or humidity sensors can be used for monitoring environmental conditions. The sensors
all share the same terminals (+5V, Ground, Data) and up to three sensors can be connected. The
sensors are able to share the same terminals without interference because they communicate with
WebSwitch Plus™ using a digital bus called the “one-wire bus” which was developed by Dallas
Semiconductor. Every sensor on the one-wire bus is assigned a unique serial number when it is
manufactured. That number is used to address the device during communication.
The sensors have three wires; the wire color is explained below.
Sensor Wire Color
Connection
Red
Vout
Black
Gnd
Blue (or White)
Data
Multiple sensors can be connected in two ways. They can all be directly connected to the unit, or they
can be “daisy chained” as shown in Figure 2.2g.
Many factors will determine the maximum length of cable used to connect sensors to WebSwitch Plus™.
Some of these factors include, but are not limited to, the type of cable used, the number of sensor,
ambient electromagnetic noise, and sensor network topology. Combined cable lengths to all sensors of
600 ft using Cat 5e cable have been successful. However due to the uniqueness of installation
environments, results may vary. Please test in the desired environment before permanent installation.
The following are general recommendations that will maximize sensor runs and minimize problems.
Cat 5 and Cat 5e network cable have proven to be an effective and low-cost solution for long runs. Other
cable types can be used, but cable capacitance may limit length. Figure 2.2h shows the recommended
connection using Cat 5 network cable.
Xytronix Research & Design, Inc.
17
Figure 2.2f - Temperature Sensor
Figure 2.2g - Direct Connection and Daisy Chain Connection
Figure 2.2h - Recommended connection using Cat 5 cable
